1. Field of the Invention
The present invention relates generally to an impact absorbing type steering column apparatus, and more particularly to a technology capable of making a collapse load variable.
2. Related Background Art
If an automobile collides with other automobile or a structure etc, a driver might suffer a secondary collision with a steering wheel by its inertia. The automobiles manufactured over the recent years broadly take an impact absorbing type steering shaft and an impact absorbing type steering column apparatus for the purpose of preventing the driver from being injured in that case. The impact absorbing type steering column apparatus is structured such that the steering column gets separated with the steering shaft when the driver suffers the secondary collision, and normally gets collapsed simultaneously with the steering shaft, and a collision energy is absorbed on that occasion.
What has hitherto been known as an collision energy absorbing system is a mesh system for causing a compression buckling deformation of a mesh member formed in a part of the steering column. As disclosed in Japanese Patent Application Post-Exam Publication No. 46-35527, however, there has been widely adopted a ball system in which metal balls are interposed between an outer column and an inner column and act to form plastic grooves in an inner peripheral surface of the outer column and in an outer peripheral surface of the inner column when collapsed.
Further, a drawing type system disclosed in Japanese Patent Application Laid-Open No. 7-329796 has also been taken over the recent years. A drawing type collision energy absorbing mechanism takes such a configuration that one side end of an energy absorbing member composed of, e.g., a band-like steel plate is fixed to a car body sided bracket, and a drawing member such as a steel rod etc fitted in a buckling portion formed in the energy absorbing member is provided on the side of the steering column and causes a drawing deformation of the energy absorbing member when the steering column shifts forward.
Moreover, a tear-up system disclosed in Japanese Utility Model Publication No. 5-68776 has partly been adopted. The tear-up type collision energy absorbing mechanism takes such a configuration that a central portion of the energy absorbing member composed of, e.g., a band-like steel plate is fixed to the car body sided bracket, two side portions of the energy absorbing member are fixed to the steering column in a way that bends it in a U-shape, and the energy absorbing member is torn up while being deformed by bending when the steering column shifts forward.
By the way, in each of the impact absorbing type steering column apparatuses described above, the steering column becomes collapsed when a predetermined collapse load acts, however, this collapse load is normally set based on a kinetic energy generated when a driver having a standard weight secondarily collides with the steering wheel. If the driver is a small-sized women and when a car speed is low, however, as a matter of course, the kinetic energy thereof decreases, and the energy absorption quantity can not be adjusted corresponding to a driver's physique, a car speed etc.